Air control instrument



Feb. 13, 1945. H. s JONES AIR CONTROL INSTRUMENT Filed July 5, 1940 3Sheets-Sheet 1 INVENTOR.

HARRY S. JONES TT ORNEY Feb. 13, 1945. JONES I 2,369,571

AIR CONTROL INSTRUMENT Filed July 5 1940 3.Sheets-Sheet 2 0 ea 5|FlG.'2.

ea 80' as INVENTOR.

HARRY s. JONES Feb. 13, 1945. s JONES 2,369,571

AIR CONTROL INSTRUMENT Filed July 5, 1940 A 3 Sheets-Sheet s PRESSURE 5734 INVENTOR.

HARRY S. JONES WORNEY Patented Feb. 13, 1945 AIR CONTRQL INSTRUMENT mms. Jones, Philadelphia, Pa., assignor to The Brown Instrument Company,Philadelphia Pa.,-

a corporation of Pennsylvania v Application July 5, 1940, Serial No.344,185 2 Claims. (o1. isv issi The present invention relates to thecontrol'of a variable condition by means of a pneumatic instrument thatis responsive to both the change of the condition from a normal valuethereof and to the rate at which the condition is changing. For purposesof illustration the condition described herein which is being controlledis tem-.

perature, but it will be readily apparent to those skilled in the artthatrthe instrument is adapted equally as well to control othermeasurable conditions such as, for example, pressure and flow. It has,in the past, been dimcult to maintain the value or the temperature ofsome mediums at a constant value because of the process lag. That is,the timethat is required for a change in the temperature to take placeas a result of a change in the heat supply. The slower the value of thetemperature changes the more diflicult it has been to maintain controlthereof and the longer it took to return the temperature toward normal.

The invention herein is an improvement in instruments or the type thatare responsive to the rate at which the temperature is changing as wellas to the amount and direction of the change. The instrumentis simple inconstruction andeasy. to 'install in systems that are already set up.The instrument is an air control instrument provided with a numberor'adjustments, the use or which permit the'instrument to be applied toa large number of control applications. These adjustments may be so ar-,ranged that the output pressure of the instrument will vary for a giveninput pressure and the range of the output pressure can bevaried for agivenrange of input pressure. The output pressure is then applied to acontrol valve.

It is an object of my invention to provide improvements in rateresponsive control instruments of the type that supply a control impulsewhich is proportional to the rate at which the t'erriperature beingcontrolled is changing to thereby -quickly counteract the change andreturn the temperature to normal.

It is a particular object of the invention to have a pneumaticinstrument or the type mentioned that has on it adjustments to vary; the

span" and the zero or the instrument. In

. other words to provide an instrument in which which the control valvemoves from opened to closed positions, than is usually permissible. In aprocess that has an appreciable lag the instrument of my inventionpermits the control system toanticipate and cancel a considerable.

part of this lag. The use of ,a rate response re-. sults in a narrowerthrottling range without encountering hunting of the controlledtemperature.

It is a further object or my invention to provide improvements inmeasuring instruments of thetype that are responsive to the rate ofchange of a variable condition to becontrolled, which instrument maybeadded to existing control installations to improve the quality of thecontrol obtained thereby. I

The various ieatures of novelty which characterize my invention arepo'inted' out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,however, its advantages and specific objects attained with its use,

reference should. be had to the accompanying drawings anddescriptivematter in which I have illustrated and described a preferredembodiment of the invention.

In the drawings:

Fig. 1 is a view of a control system incorporating the instrument or myinvention showing the control of the outlet temperature of the oil inacracking still;

' Fig. 2 is a view or the component parts of the rate responsiveinstrument;

Fig. 3 is an enlarged view of a portion or the rate responsiveinstrument; g r

Fig. 4 is a detail .view .of a portion of the primary control instrumentof the system of Figure 1; and

It is a further object of my invention to provide improvements ininstruments which permit the use of a much narrower throttling range, orrange of variation of the temperature through Fig. 5 shows two curvesthat illustrate the operation of the instrument.

Referring first to Figure 1, there is shown a iumace I that is used toheat oil flowing therethrough in pipe 2'. This oil is forced through thepipe or tube 2 by a constant speed pump 3. The process in which the hotoil is used. requires that the temperature at which it leaves the fur--nace be maintained constant and this is accomplishedby varying thesupply of fuel to the furnace. It is customary to control the supply offuel, generally oil, by means or any suitable type or how controllerandto vary the control point of this controller in accordance with the exittemperatureof the oil. Due to the large volume of oil flowing throughthe pipe 2 and the large diameter of this pipe and to changes in the oilinlet temperature, there has been considerable lag between the time thata change in the temperature of the oil was detected and the time thatthis change was corrected. If, however, the control instrument iscapable of taking into account the rate at which the temperature ischanging, as well as the fact that a temperature change has occurred,suitable corrective action may be taken to more quickly return the oiltemperature to normal. v

The temperature oi: the oil as it leaves the furnace l is measuredby athermocouple 4 placed in the pipe 2, which measurement is recordedplying air at a suitable and approximately constant pressure. through arestricted passage formed by a small bore pipe 29, included in a pilotvalve mechanism 30, so that the pressure in the nozzle 25, whichconstitutes the primary control by an air control potentiometerindicated generally at 5. This potentiometer varies the pressure or asupply oi air in accordance with this measurement, and applies thevariable pressure to the rate responsive instrument indicated generallyat 8. Fuel is supplied to the furnace l through a pipe 1 having an airactuated valve in it. The flow of fuel is controlled by a flowcontroller indicated generally at 9 which controller supplies air undervarying pressure to a valve positioner l which in turn controls thepressure oi air supplied to the diaphragm of valve 8. The rateresponsive instrument 8 may be used tosupply air under varying pressureeither directly to the valve positioner or, more generally, may be usedto adjust the control point of the flow controller 9. It will,therefore, be seen that the fuel is controlled by the instrument 9 tomaintain a given flow thereof. This flow is then changed in response tochanges in the outlet temperature of the oil, as measured by theinstrument 5, through the intermediary of the instrument 6 whichsuperimposes a rate component upon the value component of instrument 5.

The potentiometer control instrument is of a yp in wide commercial useand known as the Brown Potentiometer." The details of the potentiometterstructure form no part of the invention herein since they are shown andclaimed in Harrison et al. Patent Number 2,150,502, and Harrison PatentNumber 1,948,280. It is sufllcient to say that a pen carriage H movesback and forth across a chart I! to make a record thereon in response tomeasurements made by the thermocouple 4. tiometer are produced as aresult of the mechanical interaction of a roller I 3 on the pen carriageN (Fig. 4) and a control table part l4. In the arrangement shown in Fig.4, the angular ad- 'iustment of the part l4 about its pivotal axis l5,

operativeiy adjusts the flapper valve of an air controller elementincluded .in the instrument 8, through connections of the characterdisclosed and claimed in the patent of Coleman B. Moore. Number2,093,119, granted September 14, 1937. Those connections comprise a partI! connected to the part l4 to share the oscillatory movements of thelatter, a link I! connecting the part It to one arm of a rocking elementI9, and a link I! connecting a second arm of the element II to theflapper valve actuating element of the air oontrollen,

The air controller shown in Fig. 4, is of a form fully disclosed in theColeman 13. Moore Patent Number 2,125,081. ranted July 28, 1938, and nowin extensive commercial use. The actuating member 20 is a lever pivotedat 2| to an adjustable fulcrum member 22, in the form of a lever having.a stationary fulcrum pivot 23. The movements or the lever 22 move aflapper valve 24 away from, or permit it to approach a nozzle or bleedControl eflects from the poten-v pressure 01' the control apparatus,increases and decreases as the flapper valve 24 moves toward and awayfrom the nozzle. The primary control pressure is transmitted by a pipe3! to a chamber 92 oi the pilot valve mechanism. One wall it of thatchamber 32 is movable, and with a second and smaller bellows, separatesthe chamber 88 from a second pilot valve chamber 3 5. The pressure inthe latter is produced by a valve t5 that is fastened to a spring member36 which acts as a hinge. As the pressure in chamber 32 increases thebellows 33 is collapsed and this acts through a nozzle 31 to move thevalve 85 away from an inlet nozzle 31a to increase the pressure inchamber 34. If the pressure in 32 decreases the bel lows 33 will expandand move the nozzle-Bl away from valve 85 and thereby let chamber 3%communicate with the atmosphere to reduce the pressure therein. Thepressure in the chamber 35 is thus maintained in constant proportion tothe primary control pressure in the chamber 32, and constitutes theultimate control pressure of the apparatus.

Bald ultimate control pressure is transmitted by a pipe flute theinstrument 6. The ultimate control pressure is also transmitted by abranch pipe 39 to mechanism 49, forming a part of the control apparatus,and adapted, following and as a result of each initial change in theultimate control pressure, eiiected through lint: id, to give the lever22 an initial tollow-up adjustment. and a delayed compensatingadjustment. The followup adjustment neutralizes a, portion of theinitial adjustment of the flapper valve 24. effected by the link It. Thedelayed compensating adjustment slowly neutralizes more or less of theeldest of the preceding follow-up adjustment.

Themechanism it comprises bellows elements, two of which are connectedby a connected rod 4I', which carries a projection A2. The latter actson lever 22 through a lever 43 pivoted at as, and a pin 45 interposedbetween the lever 22 and i3.

. The pin 45 is supported by a member 46 adjustable to vary the leveragewith which the lever it) acts on the lever 22. The latter is biased formovement in the clockwise direction, as seen in Fig. 4. Details of theconstruction and operation of the mechanism 40, not specificallyreferred to herein, will be understood by those skilled in the art fromthe drawings, and need not be described ,herein, particularly as thatmechanism is not .only fully disclosed in Patent Number 2,125,081,

issued to Coleman B. Moore, but is in extensive use.

I; the change in temperature is large the varia- .tion in the airpressure is large. This pressure is applied through pipe 38 to the rateresponsive in- .strument B, which serves as a pneumatic relay to apply apressure to the final control unit that is proportional to both thechange in the temperature and its rate of change.

The mechanism or theinstruinent 8 is shown in detail in Figures 2 and 3,and comprisesgen-.

. put unit 52 and the pilot valve unit 53 thatidentical with the pilotvalve 38 that has been described in connection with Figure 4.

Air from the pipe 38 enters the'instrument 5 and is applied throughbranch 38A to the interior. of a chamber 54 in the input unit. Thischamber. is provided with a flexible wall 55 that may take the form of abellows and which has a rod 58 attached to its inner end. This rodextends through an opening in a supporting member 51 and is providedwith a pair of enlargements 58 and 59-; between each of which and themember II is a spring 80 and 8| respectively. These springs tend tomaintain the bellows at some predetermined length which will..bedirectly varied in accordance with the pressure applied within thechamber 54. The outerend of the rod 58 is connected-by a link 82 withone arm of. a bellcrank lever 83 that its pivoted at 84 on a part of therate responsive unit. It will, therefore, be seen that an increase inpressure in pipe 38 will produce a clockwise-movement of bellcrank 83around84. H

Air from pipe 38 also passes through a branch 383 to the rate responsiveunit. This unit com prises a supporting member 85 upon the left side ofwhich is attacheda cup-shaped member 88 and two'bellows 81 and 88 thatserve to form a pair of chambers 89 and I8. To theright side of thesupport is a similar arrangement forming chambers II and I2, the formerof which isin free communication with the atmosphere and is providedwith a spring I3 that serves to 'put arr initial compressive forces onan outer bellows I4. The right-hand inner bellows I5 is connected by arod I8 to the left-hand inner bellows'88 so that these bellows areconstrained to move together and they are urged to a predeterminedlength by springs I1 and I8, respectively.

' The chambers I8 and I2 are filled .with an incompressible liquid' andare in communication through a pipe I9 that is provided with anadjustable valve 88. A change in pressure in the chamber 89 will then betransmitted through the liquid in chamber I and connecting rod I8 tochamber-12. Since chamber II is in communication with the atmosphere thepressures in chambers I8 and I2 will be different but will eventually beequalized by the action of springs 11 and I8 on their respectivebellows. This equalization will cause the rod I8 to return to itsoriginal position and will take place over a period of time dependingupon the opening of valve 88. I

8 Movement of the rod I8 serves to shift the pivot point 84 of thebellcrank 83 by means of the engagement between a projection 8| on therod I8 and a lever 82 that is pivoted at 83. As the lever 82 moves itmoves a lever 84, upon the lower end of which is' mounted the pivot 84.around its pivot 85 through the intermediary of a pin 85.,

.levers 82 and 84 and thereby changing their leverage. This isaccomplished by having the pin 88 mounted onzthe lower end of a member81 that isin turn attached to a plate 88. This-plate aaoasu is providedwithratchet teeth .on one face that mesh with a pinion89 which may berotated to raise and lower the pin 88.

From the above it will be seen that an increase in the pressure inchamber "I8 will cause an immediate movement oi. pivot point 84 to theright an amount proportional to the pressure change and. the position ofpin 88. .This movement will be cancelled by theslow return of the rod in18 and pin 82 to their original positions due to the action of springsII and 18 in equalizing the pressure in chambers I0 and I2. As point 84moves to the right the bellcrank 83 will move clockwise around itsconnection with'link 82.

Therefore, an increase in pressure in pipe 38 will produce a clockwisemovement bellcrank 83 that is thesum of the movements of rods 58 and 18.

Of this movement the component'due to rod 58 is permanent while thecomponent due to rod .20 I8 is transitory.

As bellcrank 83 is moved it adjusts the output unit 52 through a link'98 that is connected at its upper end to the generally horizontal arm ofthe bellcrank. -The unit 52 serves to produce a pressure that isproportional to'the movement of link 90 and is shown in detail in Figure3. The output unit 52 shown in Fig. 3, is similar in many respects tothe air controller shown in Fig. 4, and comprises parts 28 to 21, and 4|to 3 48,v similar to the correspondingly designated parts of Fig. 4. Thenozzle of Fig. 3 is in-- tended to receive air from a supply pipe, or beassociated with a pilot valve mechanism like the pipe 3] and pilot valvemechanism of Fig. 4.

The output unit 52 shown in Fig. 3 is of a type and form, also disclosedin the said Patent Numiii) ber 2,125,081, which lacks the compensatingprovisions of the aircontroller shown in Fig. 4, but includes afollow-up adjustment mechanism.

The follow-up mechanism 9| of Fig. 3, comprises i a 'bellows 92subjected externally to the controlling air pressure transmitted to themechanism from the pilot valve by the pipe 93. The tendency of thebellows -9,2, resulting from its own resiliency, to maintain a constantlength, is supplemented by the action of springs 84 and 95. The plunger4| secured at one end to the movable end wall of the bellows 92, carriesa' projection "and asthe bellows 92 elongates and contracts, it effectscorresponding adjustments of the lever 22 through a thrust transmittingconnection between the lever 22 and the plunger projection 42. Thethrust connection comprises a wedge shaped thrust block 98 pivotallysuspend-,

ed from an adjustable support 91, and lever 43.

The wedge shaped member 98 may be shifted by adjusting a pinion member98 to move the support 9! around its pivot 99. This adjustment 'servesto vary the zeroiof this unit. In other words the-output pressure of therate respon- I sive unit 8 can be varied for a given input pressure byadjusting themember 98. This is true because the position of flapper 24that varies the output pressure is controlled by the input pres 6 sureand the initia' position of the flapper with.

respect to the follow-up mechanism is varied by the. position 01 wedgemember 98.

The span of this unit or. amount of flapper movement to produce a fullrange of pressure may be varied by shifting the pin 45 up and downbetween levers 22 and 43 to change the leverage therebetween. This isaccomplished by mount:- ing the pin 45 on the lower end of a lever 48that is pivoted on a member IOI. The latter is member is provided on oneedge with rack teeth that mesh with a rotatable pinion I02. Both thepinion I02 and the pinion 98 are provided with calibrated dials, asshown in Figure 2, to indicate their adjustment.

The "span and "zero adjustments when taken together permit the ratecontrolinstrument to vary the total range of-the output pressure for theinput pressure. For example, it is At times it may be desirable to applythe varying pressure from the rate responsive instrument 8 directly tothe valve positioner It. Insuch a ease-the three-way valve IN isadjusted to a position in which pipe I03 is connected directly to thepipe 108 instead of to the flow controller usual to. have theseadjustments so arranged that l for zero to fifteen pounds input pressurethere is obtained zero to fifteen pounds output pressure. It ispossible, however, to so position these ad- Justments that the full spanof zero to fifteen pounds output pressure may be obtained for an inputpressure that varies from five to ten pounds.

Air under pressure is supplied to the pilot valve unit 53 from the pipe28 and is delivered at a regulated-pressure through pipe 98(corresponding to pipe 38 in Figure 4) to the outputvunit follow-upmeans, and through a pipe I08 (corresponding to pipe 38 in Figure 4)either to the final control unit 9 or directly to the valve positioner18. Both the lines 28 and I8 are shown as provided with pressure gaugesG so that the supply and output pressures may be noted. Other of thepipes may also be provided with pressure gauges if it is deemednecessary or desir-able. a

It is noted in passing that the output unit 82 of the rate responsiveinstrument 8. may be formed similar to the control unit shown in Figure4 if desired. In such a case the linl: 80 would move the lever 20.Generally speaking it is desirable to have the reset function that isprovided by the instrument shown in Figure4', in any control system. Ifthe primary control instrument 8 does not have the reset function, thenan output unit having that function can be substituted for the unit 52that is shown herein as having only the matically in a manner fully setforth in the patent of Coleman B. Moore, Patent No. 2,218,148, grantedOctober 1, 1940. The air from the rate responsive unit is applied, asdescribed, through the pipe I08 to a three-way valve I04, that directsthe air, when in one position through the pipe I01, to the remotesetting device in the instrument 8. Thusthe flow controller 8 tends tomaintain the supply of fuel to the furnace l constant as long as thetemperature of the oil is constant. But when the oil temperature variesthrough pipe I 01.

In describing the overall operation of the control system it willnecessarily be treated as if the various operations take placesequentially. Itmust be remembered, however, that in air control systemsthe various pressure changes take place and the various parts movepractically simultaneously. This rapid and continuous movement of thevarious components of the system is one of its advantages and one reasonwhy air control systems are in such extensive use today.

In a description of the operation it is assumed that the value of thetemperature, and therefore the various pressures in the system have beenconstant for some time and-the system is in equitlibrium. Assume, forexample, that the oil exit temperature decreases and that this, throughthe instrument 8 produces an increase in pressure in pipe 38. Thisincreased pressure will be applied through branch 38A to chamber -84 tocompress bellows 55 an amount proportional to the decrease in oiltemperature. This will produce clockwise movement of bellcranlz 55 and acounter-clockwise movement of member to in the have its control pointremotely adjusted pneu- "5 the rate responsive unit will supply airunder a a pressure proportional to the temperature change and its rateof change to vary the control point of the flow controller and thus varythe fuel supply in a direction to return the oil temperature towardnormal. The instrument 8 applies air under varying pressure throughpipes ill! and l to the-valve positional II, which is a pneumaticamplifier. now in extensive commercial use, or the type shown andclaimed in the, patent of Coleman 3. Moore, No. 2,287,038, grantedoutput unit 82 (Fig. 3). Such a movement permits the flapper 25 toapproach nozzle 25 and, through the pilot valve unit it, increase theoutput pressure as shown by curve a in Figure 5. Simultaneously with theabove the increased pressure is also applied through branch 883 to thechamber 89 to act through the liquid in chamber 10 andthe leversystemito move lint: it carrying pivot 85 to the right. This movement isproportional to the rate at which the pressure in pipe 38 increases. Aspivot point 66 moves to the right it will increase the clockwise movement of bellcranlr 88 and thereby increase the outlet pressure of theinstrument as shown in Figure 6, by the curve b. In other words thecorntrol pressure in pipe I08 will be .1

proportional to the original'temperature change by an amount equal tothe increase of curve "o above curve a.

' Theamount of pressure increase due to rate of change, or the height ofcurve a for any given rate of change'will depend upon the adjustment ofpin 86. The length of time that is required to remove the increasedpressure is dependent upon the adjustmentof valve 88 and is generallyrelated to the process lag. This meansthat the valve is so adjusted thatthe time required for the rod 18 to return to its initial position is.equal to a fraction of the time ordinarily required for the controlledvariable, or oil temperature, to stabilize at a new value, when a changehas occurred without the use of the rate responsive unit. The magnifiedresponse of the outlet pressure is thereby removed at apredetermined-rate which is based upon rate of processchange. The curvesshown in Figure 5, are produced. as was explained, by an instantaneousor non-continuous change in the value .of the temperature beingmeasureda If the change is a continuing one the complete removal of theincreased pressure shown that the change is taking place.

by curve b would be deferred during the time Thus all the time that thetemperature is away from, the contro lpoint the valve will be subj ctedto a pressure that is the algebraic sum of that produced by thedeviation of the value from the control point and the rate of its changetoward or away therefrom. v I

If the increased pressure is applied to the control point settingmechanism of the flow con-.

troller 9 the control point will be increased more than necessary andthen gradually returned to the correct point. This means that thecontrol valve positioner the action of valve 8 would have i been thesame except that the flow of the fuel would not have been taken intoconsideration. In

either event the action on the valve 8 is practically instantaneous andthe oil exit temperature is rapidly returned to normal without theoccurrence of hunting or cycling.

From the above it will be seen that the rateresponse instrument orpneumatic relay 6 is a, complete unit in and of itself that may be asreadily installed in existing control installations as it may in newones. The instrument is useful in any process where the lag is large orthe rate of change of the condition is great. The various adjustmentsprovided in the instrument permit it to be readily adapted to even themost complex control systems with an improvement of the controlcharacteristics thereof.

Another advantage that may be obtained by the use of the rate responseinstrument of this ing direction and eflectively brings the value of thecondition to the control point without hunting.

It is noted that a plurality of the rate responsive instruments maybeused in series to produce a control ofthe second or higher powerderivative.

While in accordance with the provisions of the statutes, I haveillustrated and described the best form of my invention now known to me,it will be apparent to those skilled in the art that changes may be madein the form of the apparatus disclosed without departing from the spiritof my invention as set forth in the appended claims, and that in somecases certain features'of my invention may sometimes be used toadvantage without a corresponding use of other features.

Having now described my invention; what I claim as new and desire tosecure by Letters Patent is:

1. A rate responsive air control instrument operative to set up an airpressure including a first unit responsive to the value of a conditionand adapted to insert a permanent component in said v air pressure, asecond unit responsive to the rate of change ofsaid condition andadapted to insert a transitory component in said air pressure andincluding an adjustment to vary the size of the transitory component fora given rateof change and an adjustment to vary the length of time saidtransitory component is inserted in said air pressure, and a third unitwhich is jointly operated by said first two units, a source of fiuidinvention is what amounts to a shifting of the throttling range of thesystem in an anticipating direction. As above explained the instrumentcan be so adjusted that the output pressure may vary from zero tofifteen pounds while the input pressure is varying from five to tenpounds. Such operation is produced as a result of a given movement ofthe link 90 when the output unit is properly adjusted. Since the link 90receives its movement from unit 50 in linear proportion to the value ofthe condition being measured and from unit 5| in proportion tothe rateof change under pressure adjusted by said third unit, said third unitincluding an adjustment toshift the zero point of the adjusted airpressure and an adjustment to vary the span of the adjusted air pressurefor a given adjustment of said third of the condition, the movement ofthe link for any significant rate of change is the result of twocomponents. The compound movement of linlg 90 is sufilcient to causeoperation oi. the unit 5!. prior to the time it would operate from itslinear component, therefore, the output pressure is changed earlier thanit would be without the rate response component. This early change ineffect shifts the throttling range in an anticipatunit. a i

2. A rate responsive air control instrument operative to set up an airpressure including a first unit responsive to the value of a conditionand adapted to insert a permanent component in said air pressure, asecond unit responsive of change of said condition and adapted to inserta transitory component in said air pressure. and a third unit which isjointly operated by said first two units, a source of fluidunder-pressure l adjusted'by said third unit, said third unit includingmeans to shift the zero point of the adjusted air pressure, and anadjustment to vary the span of the adjusted air pressure for a givenadjustment of said third unit.

. HARRY S. JONES.

to the rate

